Automatic electronic telephone system



April 5, 1960 A. H. FAULKNER 2,931,853

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Filed Aug. 23, 1955 15Sheets-Sheet 1 T Sm QEQSEQQ EQEQ rIY 4 L 96R 8% 2% 3a Em 2E m $33 9% 239 2 E? 1 IE is 1V L as 9% QQ wmm Q58 9% Em .35 Q6 uh QB $53 N 953% E 2%2 L a Th 9% was 2% 3 J ESQ 55 2B #3 E E =55 :St EEQ I: 9 95 3 a? $3 m \1:53. $E$$ w as we: I\ 53 r S Wm N w%\ \Q INVENTOR. ALFRED H HULK/Vt? BYv 7775- 15 Sheets-Sheet 2 A. H. FAULKNER AUTOMATIC ELECTRONIC TELEPHONESYSTEM n mm r m N A Z m H n I F L H A S m m 5% E53 N w n v m u U Al. m8% Q 9% Hum 52% 3 E J n I 82% En i 5% $3 1 8 Q EL 9% E 3 Q8 qfi Y Rn Ewe $3 $5: QEESM SQ 5 ll hi: 8% 4 as NQQ Ill |$B3Q N E m9 Em g April 5,1960' Filed Aug; 23, 1955 U Zm April 5, 1960 Y A. H. FAULKNER 2,931,863

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Filed Aug. 23, 1955 15Sheets-Sheet 3 srAr/0/v APPARATUS FROM OTHER Ll/VE GIRCU/TS l/V MULZ'TENS MARK CIR. 340

OTHER U/VE CIRCUITS //V MULI UNITS MARK/N6 CIR. 360

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April 5, 1960 A. H. FAULKNER AUTOMATIC ELECTRONIC TELEPHONE SYSTEM FiledAug. 23, 1955 15 Sheets-Sheet 4 April 5, 1960 A. 'H. FAULKNER 2,931,863

' AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Filed Aug. 23, 1955 15Sheets-Sheet 5 SM4Q .5 6 ourpur 844(8) FHG E I IN V EN TOR. ALF/FED Hl-ZULKME'R F195 8 ML 15 Sheets-Sheet 7 A. H. FAULKNER April 5,1960

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Filed Aug. 25, 1955 INVENTOR.ALF/7E0 H. HULK/VB? Wd P 5, 1960 A. H. FAULKNER 2,931,863

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Filed. Aug. 25, 1955 15Sheets-Sheet 9 70 OTHER REGISTER l l I l REGISTER w FROM OTHER LINKC/RS.

FROM OTHER SEQUENCE SWITCHES A 53 (5) RING/N6 CONTROL 956-! MATRIXDISTRIBUTOR .950

TO OTHER LINK CIRCUITS IN V EN TOR. ALFRED H. FZIUL/(IVER April 5, 1960A. H. FAULKNER AUTOMATIC ELECTRONIC TELEPHONE SYSTEM 15 SheetsSheet 11Filed Aug. 23, 1955 5 R m m m m n J m5 IB M 2m .lll' 0 mm 21 fl 6 W 7 HMm5 \NQQ m llll 3v R \E A .7

6 v IE 3s 8 z a 1|: 7 5w 8% Ti I \6 6k w 7 wow\ J a all 1% mm Emmi J MSNC \C .C 8 f 6 m .2 w Q E April 5, 1960 A. H. FAULKNER AUTOMATICELECTRONIC TELEPHONE SYSTEM 15 Sheets-Sheet 12 Filed Aug. 23, 1955 5 Rv/ R guns 6 m W H Emu m w 3 V M vi mg Em NE E m E m M Ems OR A use E 6RS :5 33 8 NNN\ VNWQ l m8 2 smv ll 1.. j 6 1| I l. J ONE i. 3% :z: wv m5Em II I II E a m5 6 I6 k5 kQm 6 2m .wmm 6 E n5 RQG 6 JL m 2E Ell A. H.FAULKNER AUTOMATIC ELECTRONICTELEPHONE SYSTEM 15 Sheets-Sheet 13 April5, 1960 Filed Aug. 25, 1955 m MK TM 2 A, m d 0 W j A Q3 mi 36x \R z m? BI $5 $1 2 Em C e 9h 9% $5 $2 #5 TS Apnl 5, 1960 A. H. FAULKNER AUTOMATICELECTRONIC TELEPHONE SYSTEM 15 Sheets-Sheet 15 Filed Aug. 23, 1955 .5050x23 mo mmosozozooW: u 23 INVENTOR. ALFRED H. FAULKNER ATTY.

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Alfred H. Faulkner, Chicago, Ill.,assignor to General Telephone Laboratories, Incorporated, a corporationof Delaware Application August 23, 1955, Serial No. 530,085

8 Claims. (Cl. 179-15) This invention relates to automatic electronictelephone systems and particularly to an electronic telephone systemutilizing semi-conductor diodes and transistors.

A general object of the invention is to provide an improved automatictelephone system for selectively establishing a two-Way communicationpath between any two telephone lines in the system.

Another object of the invention is to provide an improved automatictelephone system utilizing semi-conductor diodes and transistors toperform routing and switching operations.

Another object of the invention is to provide in an automatic telephonesystem transistor circuits responsive to line identifying signals forselectively completing connections between subscriber lines.

A further object of the invention is to provide an improved automatictelephone system employing time multiplex means for signal transmission.

A further object of the invention is to provide an automatic telephonesystem having an improved electronic switching matrix for selectivelyconnecting any one of the subscriber lines to available switchingcircuits.

A more specific object of the invention is to provide an electronictelephone system having an improved switching matrix for connecting anyone of the subscriber lines to available switching circuits on a pulsemultiplex basis.

An additional object of the invention is to provide an improved ringingcontrol circuit.

A more specific object of the invention is to provide an improvedringing control circuit particularly adapted to operate in asubstantially electronic telephone system.

A more specific object of the invention is to provide an electronicringing control circuit substantially in the form of a matrix adapted totest any subscriber line in response to the application thereto of acorresponding timed identity pulse.

Another object of the invention is to provide improved electronicdistributor circuits for selectively interconnecting the switchingcircuits in a telephone system.

A more specific object of the invention is to provide improvedelectronic distributor circuits for interconnecting switching circuitsin a telephone system substantially in the order that the distributor isseized by an incoming switching circuit.

Another object of the invention is to provide an improved line circuitfor use in electronic telephone systems. A more specific object of theinvention is to provide an improved electronic line circuit particularlyadapted to operate in an electronic telephone system employing pulsemultiplex transmission means.

Further objects and features of the invention will be understood fromthe following description and drawings, forming a part thereof, wherein:

Figs. 1 and 2 show in block schematic form an automatic telephone systemin accordance with the invention;

Figs. 3 through 10 comprise a detailed circuitdiagram of the telephonesystem illustrated in Figs. 1 and 2;

. United States Patent ice Fig. 11 illustrates the manner in which Figs.3 through 10 are joined to form the composite circuitdiagram;

Figs. 12 and 13 display a schedule of the voltage and currenttransformations that take place in the telephone system responsive tothe initiation of a call therein; and,

Figs. 14 and 15 are schematic diagrams of alternative circuits for usein the telephone system of Figs. 3 through 10.

Fig. 16 is a schematic diagram of the two-way transmission systemaccording to the invention.

Section 1The general arrangement of the telephone system Referring moreparticularly to Figs. 1 and 2 which are joined in end-to-endrelationship for viewing purposes, there is shown therein in blockschematic form, a telephone system operated on a step-by-step basis toestablish selectively a two-way communication path between any twosubscriber lines, for example; subscriber lines 301 and subscriber line711, in a group of subscriber lines and to maintain a plurality of suchcommunication paths at a time. The system includes an in-switchingmatrix 450 which has access via the line circuits, for example, the linecircuits 320 and 720, to all of the subscriber lines in thegroupincluding the subscriber lines 361 and 711 for connecting the callingones to the common conductor SM469 on a time division basis. The markingcircuits 340 and 360 have access to all of the ins circuits in thetelephone system and therethrough identify the calling ones of thesubscriber lines on a oneat-a-tirne basis. The identity of a callingline is transferred to an idle one of the pairs calling tens and unitsregisters of which only two pairs 810 and 830, and 810A and 839A areillustrated. A register distributor 910 continuously assigns an idle oneof the pairs of registers to the marking circuits. The individual pairsof registers operate to efiect connection of the correspondingsubscriber lines to the common conductor SM460 during selected periodsof a timed cycle which selected periods are reserved to the exclusiveuse of the register pair by the pulse generator 850. V

A number of link circuits 500, etc., which are individually assigned tothe pairs of registers and operated in synchronism therewith by thepulse generator 850, each recover the signals of one of the callingsubscriber lines from the conductor SM460, identify the calledsubscriber line and transfer the connection to the common conductorSM62tl. A ringing control matrix distributor 950 assigns the identity ofa called line to the ringing control matrix 750 on a one-at-a-time basiswhereby the calling subscriber line is tested for busy or idlecondition.

' An out-switching matrix 600 has access to all of the subscriber linesin the group and also to the conductor SM620 for completing theconnection between calling subscriber lines and called subscriber linesduring the selected periods of each timed cycle. 1 A ringing machine 860provides means for ringing any idle subscriber line responsive to thetest thereof by the ringing control matrix'750.

Section 2-The apparatus incorporated in the telephone system The severalsubscriber lines 301, 711, etc., are pro vided with conventional stationapparatus 300, 710, etc., including ringing and speech equipment andline circuits 320, 720, etc. Assuming that the system, as describedhereinafter in detail, is adapted-to serve one hundred lines, thesubscriber lines thereof are identified by two digit directory numbersof which the directory number for subscriber line 301 is arbitrarilychosen tobe 01' and the directory number for the subscriber line 711 isarbitrarily chosen to be "1 l. The line circuits operate to complete aconnection between the subscriber line and the in-switching apparatusincluding the tens marking circuit 340 and the units marking circuit 360and the in-switching matrix 450 when the line is calling and to completea connection between the out-switching apparatus including the ringingcontrol matrix 750 and the out-switching matrix 600 and the subscriberline when the-line is called.

. The tens marking circuit 340 and the units marking circuit 360 arecommon to all of the line circuits in the telephone system and eachincludes ten interconnected stages respectively numbered from 1 throughwhich stages are operable one at a time over input conductorsrespectively corresponding ,to the stages. Thus, each of the stages inthe tens marking circuit 340 is connected via the corresponding inputconductors LT-l, LT-2, etc., to the groups of'line circuits for whichthe tens digit of the directory number corresponds to the number of thestage. By way of example, the last or stage in the tens marking circuit340 is connected via tens conductor LT-O in multiple to the linecircuits (including the line circuit 320) of the subscriber lines forwhich the tens digit of the directory number is 0. Similarly, each ofthe stages in the units marking circuit 360 is connected via the inputconductors LU-l, LU-2, etc., to the groups of line circuits for whichthe units digit of the directory number of the subscriber linescorresponds to the number of stage. By way of example, the first or "1stage of the units marking circuit 360 is connected via the unitsconductor LU-l in multiple to the line circuits (including the linecircuit 320) of the subscriber lines for'which the units digit of thedirectory number is 1.

In order to provide markings from the circuits, the tens marking circuit340 includes the output conductors MT-l, MT-2, etc., respectivelycorresponding to the stages and which are connected to the correspondinggroups of line circuits and to the multiple conductor trunk line MTextending to the calling tens registers 810, 810A, etc. Specifically,the output conductor MT-0 is connected to the trunk line MT and to thegroup of line circuits (including the line circuit 320) of thesubscriber lines for which the tens digit of the directory'number as "03The latter connection activates the connected line circuits to permitthe application of a calling line marking signal on the one of thecalling line circuits to the corresponding one of the input conductorsLU-l, LU-2, etc., extending to the units marking circuit 360. .1 In theunits marking circuit, the output conductors 'MU-l, MU-2, etc., areconnected to the multiple conductor trunk line MU extending to thecalling units registers 830, 830A, etc.

Thus, the initiation of a call on subscriber line 301 causes the tensconductor LT-O of the line circuit 320 .to' be marked by a signalingvoltage. The LT-0 conductor extends to the 0 stage of a tens markingcircuit 341! and when no other stage in the marking circuit is active, asignaling voltage is returned to the line circuit 320 via the tensmarking conductor MT-0 to control the line circuit for applying asignaling voltage on the units conductor LU-l extending to the 1 stageof the units marking circuit 360. The 0 stage in the mark ng circuit 340and the 1" stage in the marking circuit 360 are therebyoperated andresponsive thereto to the conductors MT-0 and MU-l extending to thecalling tens and units registers via the trunks MT and MU, respectively,are marked. In the calling registers, the identity of the one callingline is registered and the marking circuits are subsequently caused tobe released from the line circuit of the one calling line in a manner tobe described more fully hereinafter.

It 18 to be noted that the foregoing explanation of the marking of theidentity of a calling line is predicated on but one subscriber line inthe system initiating a call at any one time. The operation of the tensmarking circuit 340 and the units marking circuit 360 is the same evenif more than one subscriber line should initiate a call at the sameinstant except that the marking circuits 340 and 360 provide an order ofpreference, as explained more fully hereinafter, so that only onecalling subscriber line can be identified therein at any one time.

The calling tens and units registers 810 and 830, etc., are arranged inpairs and in addition to registering the identity of a callingsubscriber line, each pair selectively operates the in-switching matrix450 to connect the corresponding calling subscriber line to the singleconductor output lead SM460. In the exemplary telephone system there areten pairs of individually numbered tens registers and units registerswhich are represented in Fig. 1 by the No. 1 calling tens register 810and No. 1 calling units register 830, and the No. 10 calling tensregister 810A and the No. 10 calling units register 830A. Idle pairs ofregisters are assigned to the marking circuits 340 and 360 on aone-at-a'time basis by a register distributor 919. The presence of tenpairs of registers permits the telephone system to handle ten callinglines at a time. The pairs of registers are sequentially activated intimed cycles by pulses applied thereto from the pulse generator 850whereby the calling subscriber lines identified in any one of the pairsof registers are connected through the register controlled in-switchingmatrix 450 during the activation periods corresponding to the onecalling register pair to the output lead SM460 on a time sharing, ortime multiplex'basis.

The in-switching matrix 450 comprises a plurality of selectivelyoperative cross points respectively corresponding to the subscriberlines in the system for interconnecting individual ones of thesubscriber lines to the inswitching matrix output lead SM460. All of thepairs of calling registers having access to all of the crosspoints andeach busied pair of calling registers operates, during its activationperiods, the one crosspoint corresponding to the calling subscriber lineidentified in the pair of calling registers thereby connecting via thecorresponding line circuit the calling subscriber line to the outputconductor SM460. Immediately after the connection between the callingline and the lead SM460 is completed, the line circuit is operated toremove the marking voltages from the marking circuits" 340 and 360whereby the marking circuits are released therefrom and prepared toidentify another calling line.

By way of an example, assume that the calling subscriber line 301 isidentified in the marking circuit 340 and 360 and that the correspondingdirectory number 01 is registered in the idle No. l calling registers810 and 830 arbitrarily assigned thereto by the register distributor910. Responsive to the registration of the directory number 01 thereinthe No. 1 calling registers 810 and 830, which are activated in thistime multiplex system 'for one fixed period out of every ten periods,for example, the first five microseconds of a fifty microsecond period,operates during the five microsecond activation periods, the crosspointin the in-switching matrix 450 corresponding to the calling lineidentified by the 01 directory number. The operated crosspointinterconnects the matrix output lead SM460 with the calling subscriberline 301 via conductor L401 and the line circuit 320. As soon as thecallingsubscriber line is connected through to the matrix outputconductor SM460, the marking voltage inthe line circuit 320 is removedfrom the LT-0 conductor thereby releasing the marking circuits 340 and360 and rendering the marking circuits available to identify othercalling lines. I

The conductor SM460 has access to a plurality of link circuits 500,500A, etc., respectively corresponding to the pairs of calling registerswhich link circuits are correspondingly numbered and cyclicallyactivated in'synchronism with the corresponding pairs of callingregisters. Thus, for example, the No. 1 circuit 500 is associwith,thesconductor' SM 46,0. during the same fivi; microsecond intervals thatthe corresponding No.. 1' calla. ing;registers 810 and 830 connect thesubscriber line 301 t'cntheconductor SM460.

Each of the link ,circuitshas a plurality of individual circuitscorresponding to those shown in detail in the: No. 1 link circuit 5000fFigs. 5, 6 and 10 including an. input control circuit 513, a. holdingcircuit 514; sequencev switch. 540, tens counting chain 1000, unitscounting chain 1050 and a switch-through circuit 650. Common to all ofthe link circuits. are the ringing control matrix distributor. 950 and aringing control matrix 750.

.Ineach of the link circuits, the directory number dialed" at thecorresponding calling subscriber stationis: recovered and registered.For example,v assuming that the subscriber line 301 initiates a call tothe subscriber. line: 711 identified by the directory number 11;the. No;1' link circuit500 'recoversand registers the: directory number 11transmitted to it via the in-switching matrix 450 and the-conductor-SM460. Responsive to registration'of the dialed directory number in thelink circuit 500, the called subscriber line 711 identified by thedialeddirectory number,-is' tested to determine whether the line is busyoridle. This testing is accomplished through a: ringing control matrix750 which is connected directly totheline circuit720of the subscriberline 711 via the conductor RC11 in the multiple conductor trunk line RC.The link circuits identifying the called subscriber lines are assignedto the ringing control matrix 750 on' a one-at-a-time basis by" theringing control matrix distributor 950.

If the called line 711 identified in link circuit 500 is found to beidle by the ringing control matrix 750, the ringing machine 860 isconnected to the line circuit 720 thereof via the ringing generatorleads RG-1 and RG-2. Futthen in response to the answering of the call atthe called line the crosspointin the out-switching matrix600corresponding to thecalled subscriber line 711 isoperated"in'synchronismwiththe activation of link circu 500Lso that theconductor, SMdfih is connected via th' inkcircuit 0:0, conductorSMtEZithe out switcliing matrix;- 6 1 the conductor L411 and the line -ciicuit720; to the subscribeit line lll during the five microsecond intervalsthatthe callingisubscriber'line 301 is connected sine conductor SM460. jIn this manner a connection" is c'ompl'etjed from theetnin subscriberlinex301 to the. called subscriber line 711 I f Should'the called line711'be busy, the link circuit 500 is-jcaiis'edby the fringing controlmatrix 750 toreturn a busy signalftogthe, calling: line 301' over theline SM460,f whereupongthe party atsubscriber line 301 mayreleasetheconnecti'on, V 11r "To better understand the mode of operationoffthc. individual;circuitsinthe system, reference will now/bemadeitoitheliigsfi3 through arranged as shown igiFig. ill y-fway. of introduction -to,the Figs. 3 through 10,: n b efnoted th'atlhe} telephonesystem is es sejritially electronic; and includesdiodesand'ftransistors, Theitransisters. and,dio'deslused'in'fthejcircuits are prefera a lcrystalline type of asemi-conductor material, such as foifexample, germanium. The diodes are.identified irt the drawings by. thefconventional symbol whereintheelectric current flow (as distinguished from electron current flow) isfrom the anode electrode thereof i'nthe direction of the arrow *to thecathode electrode? The transistorsused in.the.,circuits. are preferablyof the junction type. and asmaylbejnoted from theconventional symbols Aemployed are of n-p n semi condu'ctor construe-f tioniLtheQarrow 'q'nvthe emitter electrode is pointediaw ay from thelbase) and ofpm psemi-conductor construction (flie'iarfow on the'emitt'er electrode ispointed" towards th base); The direction of the arrow defines thedirection. ofelectriccurrentfflowthrough the emitter. The features orthe" telephone Y system in accordance the'inveritionwill he-underst'o'o.d from thefblloivifig etc.

connected thereto via the diode D327.

menses.-

initiation of a call at the station. 300 on subscriber line 301.

Section 3--Initiati0n ofa. call at the station 300 As. shown in Fig. 3,each of the subscriber lines 301,

etc., comprises a pair of line conductors 301A and 301B, etc, havingconnected thereacross a calling station 300,

includes the telephone instrument 312 and the dial mechanism 316including the impulse springs 317 shunted by the resistor 318 and thedial off-normal springs 319.; Additionally, the station apparatusincludes the switchetc., are idle, none of. the circuits inthe system,are op.-'

erative other than the register distributor 910 which as; preselectedand assigned, for example, the idle No. 1 calling registers 810 and830to the marking circuits 340 and 360; respectively. The current flowthrough the subscriber line 301 at this time t is interrupted, whichcurrent flow is illustrated by the curve 1201 in Fig. 12.

When at the time 2 the party at station 300 removes: the telephoneinstrument 312 from the switchhook 313 for the purpose of initiating acall, a circuit is completed? from 48 volts in the linecircuit 320through the resistor: 332A, the upper primary winding of the transformerTR-l, the contacts 331A, conductor 301A, telephoneinstrument 312,switchhook contacts 313A, conductor 301B, contacts 331D, thelower'primary winding of the trans-- former TR-l and the resistor 332Bto ground potential. The values of resistors 332A and 332B are balancedwith respect to the impedance of the subscriber line and the telephoneinstrument 312 so that when the circuit is completed, the current flowtherethrough will establish.

at thejunction between resistor 332B and the lower winding of thetransformer TR-l at -'-24 volts. Inasmuchas DC. loop impedance of thesubscriber line 3013 and the'station 300 may vary, the junction betweenthe? resistor 332B and the lower primary winding of the transformer TR-lis prohibited from going more: negativethan -24 volts by the --24 voltsource This negativ'e voltage on "the one terminal of the resistor 332B-is appliedl'to'the emitter of the transistor T329 thereby renderingthis transistor conductive from groundpotential'via resistors 337A and337B and through the baseemitter path thereof; The collector electrode:

i's thereup'on clamped-av -.24"v0lt's which voltage is ex-- tendedtofl'the junction betweenthe resistors 328A andv 328B=and the diodeD334.. Responsive'tothenegative voltage; at the junction, the cathode ofdiode D334 is. biased conductive and the transistor-T338 is: biased atits conductive threshold. Inasmuch as the current flow in the loopisD'.C. there is no current. flow: induced; in. the primary-winding ofthe' transformer and" the" capacitor- 336' connected 'from onenterminalof the I secondary: winds ing to ground-potential"is notl charged;-As1no current flow is. provided through the s'econ'dary windinglor; thespeech frequency shunting capacitor i 335 ':connected :between groundpotential and the other terminaliof the. secondarywindingtoith'e-baseelectrode of transistor'l339' via contacts"- 331Ethe'transistor-T339 is nonconductive; Additionally,-no curre'nt'is drawnthrough the base elecf trode' of "transistor T326 via; the contacts"33IHand con duct'orRC- 01, hence this transistor'jis alsononconduq; tivef atthe time ti, theilarge current in the subscriber line 301 causedv bythe-initiation lot" afcall" thereon: has caused the diode D334 in theline. circuit' 320. tq'be biasedconductive and the transistor T338ftojbe raised to conduction threshold thereby marking the Subscriberlint;- sums ca lingite th ma inss cu sflfldda hewnqncg The apparatus instation 300 is conventional and menses" tor LT-O whereby the tensmarking circuit 340 the units marking circuit 360 are operated.

Section 4-0peration of the marking circuits and output conductor and isoperated only over the input conductor corresponding to the stage. Thus,in the tens marking circuit 340, the first stage is connected inmultiple via conductor LT-l to all line circuits for which tens digit ofthe directory number of the subscriber line associated therewith is 1and the stage is therefore known as the 1' stage. Similarly, the inputlead LT- to the last stage in the tens markingcircuit 340 is connectedin multiple to the line circuits, including the line circuit 320, forwhich the tens digit of the directory number of the subscriber lineassociated therewith is 0 and the stage is therefore known as the 0stage. The stages in each of the marking circuits are so inter-connectedthat only one stage in each marking circuit may be operative at anygiven time.

Referring specifically to the tens marking circuit 340;

the transistors T342-1 through T342-0 and T348-1 through T348-0 in thestages thereof are normally conductive when no marking is applied to theinput conductors thereof and the transistors T347-1 through T347-0arenormally nonconductive whereby no marking is applied to the outputconductors of the stages. Responsive to the above described marking onthe diode D334 in the line circuit 320, current flows in the conductorLT-fl from the "0 stage thereby operating the 0 stage in a mannerdescribed hereinafter and indicating that one of the subscriber linesfor which the tens digit of the directory number 0 is calling. The inputlead LT-0 to the stage is connected to a junction between the resistors341A-0, 3413-0 and 341C-0, which junction is normally maintained at theground potential via the resistor 34113-0. At the time t the -24 voltsapplied to the cathode of the diode D334, renders the diode conductivecausing current to flow therethrough and establishing the junctionbetween the resistors341A-0, 341B-0 and 341C0 at 24 volts. The potentialat this junction biases the base of the transistor T3474) conductive viathe resistor 341A-0 and diode D346-0. The collector'and the emitter oftransistor T347-0 are thereby clamped at substantially 48 volts causingthe transistors T342-0 and T3480 to become nonconductive at the emitterelectrodes thereof. Responsive to nonconduction in transistor T342-0,ground potential is removed from the collector thereof thereby changingthe path of the current flow from the base of the transistor T347-0 tothe conductor LT-0 to that path through diode D3494) and the resistor341C-0. The collector electrode of the now nonconductive transistorT3484) is maintained at substantially ground potential whereby the baseof the transistor T352 is rendered conductive and the emitter electrodeis established at substantially ground potential. The ground potentialon the emitter electrode of T352 is further extended to all of thediodes D345-1 through D345-0, thereby providing a lower impedancecurrent path to the conductors LT-1 through LT9 than is availablethrough the nonconductive transistors T347-'-1 through T347-9. Thus, atthe time t the 0 stage of the tens marking circuit 340 is renderedconductive and all of the other stages of the marking circuit aretemporarily rendered nonconductive and the output conductor MT-O fromthe "0 stage connected to the emitter electrode of transistor T347-0 isat 48 volts potential as indicated by curve 1202 in Fig. 12.

The conductor MT-.0 extends to the collector electrode at transistorT338in the line circuit 320 as well as to similar transistors in allother line circuits for which let the tens digit of the directory numberis "'0." Additionally, the conductor MT-0 extends to the assigned tenscalling register 810 via trunk MT. It is assumed that at the time t,,only the subscriber line 301 of all of the lines for which the tensdigit is 0, is calling and therefore, only the transistor T338 in theline circuit 320 will be at conductive threshold. The 48 volts appliedto the collector electrode of the transistor T338 by the conductor MT-0renders only that transistor conductive thereby clamping the emitterelectrode thereof at 48 volts. As the units digit of the directorynumber of the calling line 301 is 1, the emitter of transistor T338 isconnected via conductor LU-l to the first, or 1 stage, of the unitsmarking circuit 360. In the 1 stage of the units marking circuit 360,the 48 volts applied to the line LU-l renders the transistor T367-1conductive and the transistors T362-1 and T368-1 nonconductive in thesame manner as described above with reference to the "0 stage in thetens marking circuit 340. Additionally, therein, the collector electrodeof transistor T368-1 which is at this time nonconductive, is maintainedat substantially ground potentlal through resistor 369A-1. This groundpotential is applied to the collector electrodes of the succeedingtransistors T367-2 through T367-0, thereby disablingthose transistorsand simultaneously biasing the emitter electrodes of the transistorsT368-2 through T368-0 nonconductive. Nonconduction in transistor T368-0renders the transistor T372 conductive and establishes the emitterelectrode thereof at ground potential, thereby disabling via the diodesD3654. through D365-0, all

of the stages "2" through 0. The 48 volts at the emitter electrode atthe transistor T367-1 is applied to the output terminal MU-l which isextended to the units calling register 830 via the trunk MU as shown oncurve 1203 in Fig. 12.

Should it happen that more than one of the subscriber lines, includingsubscriber line 301, for which the tens digit of the directory number is"0 be initiating a call at this time, the transistor T338 in the linecircuit 320 and the correspondingly biased transistors in the other ofthe calling line circuits will be rendered conductive by the 48 voltsapplied thereto over conductor MT-0. As a result, the conductor LU-l andthe corresponding conductors connected to the units marking circuit 360will be marked by a 48 voltage. However, in this instance only the 1stage in the marking circuit 360 will be operated because the stagestherein operate one at a time as explained and the circuit establishesan order of preference proceeding from the "1 stage through the 0 stage.The other calling subscriber lines are delayed and identified accordingto the order of preference as the marking circuits 340 and 360 arereleased by the line circuits.

Thus at the time t the tens marking circuit 340 has identified by amarking on the MT0 conductor that a subscriber line for which the tensdigit of the directory number is 0 is calling and the units markingcircuit has simultaneously identified by a marking on the MU-l conductorthat a subscriber line for which the units digit of the directory numberof 1 is calling. These markings on the MT0 and MU-l conductors areextended to the assigned tens register 810 and units register 830,respectively.

Section 50peration of the No. I calling registers As mentionedpreviously, it has been assumed that the registers 810 and 830 formingthe No. 1 calling register pair were preassigned to the tens and unitsmarking circuits 340 and 360, respectively, by the register distributor910. The method of assignment will be explained in detail later. Each ofthe register circuits are made up of ten stages respectivelycorresponding to an output conductor from a marking circuit. Thus, thecalling tens register 810 has ten stages respectively connected to thetens mark.

geese-es in'g circuit output conductor MT-l through MT-T and: the unitsregister 830 has ten stages respectively connected:

connected to the register distributor 9 by the conductor" RD-l.Responsive to the preselection by the register distributor 910 of theNo. 1 calling registers 810 and 830 for operau'on with the markingcircuits 340 and 360 at the time t 48 volts is-applied to the conductorRD-l by the register distributor 910. This voltage is connected to allof the stages in the tensregister 810' via the resistors 817-1 through817-0 and to all of the stages in the units register 830 via theresistors 843-1 through 843-0.

In the tens register 810, the conductors MT-l through MT-0 apply groundpotential to the corresponding stages. via resistors 816-1 through816-0, respectively, and the marked conductor MT-0 applies 48 volts tothe- "0 stage via the resistor 816-0. Similarly in the units register830, the marked conductor MU-l applies 48 volts to the li stage thereofvia resistor 838-1 and the other con ductors- MU-2 through MU-0 applyground potential to tl' ccorresponding stages via theresistors 838-2through 838-0,,respectively; Thus, the' voltage in the tens register8l0at the junctionbet'ween resistor 816-0 andfresistor 817-0 is -3-2 voltsthe voltages atthe-correspondingj junctions'in the other stages of the"tens"register810'is less than -24 volts. The suddenapplication-eta"pdteii o tial greater than :24 volts -32'vo'lts)--totheicapacitor 820-0 causes a'negative impulseto be'applied tothe' baseof the transistor T8-15-0 whichsmomentarily renders thattransistor conductive. Responsive to thejconduc'tiom ithej emitteriandcollector electrodesare raisedfto ground'poj: tential. At the same time,thenegative pulseis' applied tq the, collector of the transistor T813-0'via the resistor. 814-0 andjthe'base of the transistor T813-0israisedjtofa potential intermediate between ground potential and 48;voltsb'y thecollector of transistor T815 0 via'th'e resistor-'819-0thereby rendering the transistorjTSljS-tlconductiveandfclampinglthe base and the' collectorof the transistor T81'5-0 atconduction voltage. 3 Thus, the1'transistoif T813-0 locks the transistorT815 0 conductive when'fthe latter has; been" triggered conductiveby'the applied negative pulse The -24 voltsat the other stagesintheftensregister 810 is insufiicient'to initiate conduction in the transistorsassociated. therewith. f With the "transistor T815-0 conducting theanode of the diode D8214) is'he'ld at substantially ground potentialjvia the resistor 823-01 thesame time a positive pulse PP o fl a valuein the, order of 10 volts as shown in" curve- 1204ofFig. isapplied fromthe pulse-generator 850 to. the. ano s, of diodes 12821-1 through D821-0via the capacitors 8I8-1-'tlirough 818-0, respectively. Thus, at this.time ti, fth e anodesot the diodes D821-1 through D821-9'1aref atsubstantially '-48 volts and cyclically. receive the PP pulsations whichare not transmitted therethrougli. At the same timelthe. anode of diode13821-0 is at substantially ground poten.- tial. and cyclically.receives :the positive}PP pulsations which are transmitted therethrough;to provide an output on conductor RT-"O asshort ruin curve 1205 of. Fig..12.

Similar action take's place inthe first; or flf. stagev of the callingunits register 830wherebythe transistors, 17837-1 and T836-1are renderedconductive. 'The @148 volts; on the collector electrode T836-1.isappliedtothe cathode of. diode D834-1'viathe resistor. 845-1.lAd'ditionally, the negativepulsesNP fromthe.pulse generator 850 and ofa magnitude in. theorder. of 10 oltsandof simultaneous occurrence withthe pulses PR as shown in diagram1206 of Fig. 12, are applied .tothecathodes of di0desD834-1 through D834-0 viathe capacitors. 833-1through 833-0, respectively.- At this timet theicathode .of. the diodeD834-1 in the units register; 830 is at substaue tially; -48volts andthe applied negativepulsations are transmitted therethrough to providean output on conductorRU- i asrshown irr curve fiil i of l i'g. 1 24.Attire.

through same time, the cathodes of the diodes D834-2 D834-9 are atsubstantially ground potential.

The diodes D821-1through. D821-0 of the calling tens register 810 areconnected at the cathodes thereof tothe conductors RT-l through RT-0,respectively, which are in turn connected via the multiple conductortrunk RT to: the in-switching matrix 450. Similarly, the anodes of thediodes D834-1 through D834-0 of the calling units register 830 areconnected to the leads RU-l through RU-O,

Section 6-O'peratian 0f the in-switc'hing matrix 450 The in-switchingmatrix 450. comprises: one hundred: cross-points respectivelycorresponding to the subscriber lines in the telephone'system forcompleting a connection for any calling ones of the subscriber lines tothe switching matrix output leadSM460. Each of the crosspoints includesapair of oppositely-poled diodes such as, for example, D404-1 and D405-1,a resistor such as 406-1 connectedfrom the junction between the diodesto 48 volts and a transistor T403-1 connected at its collector.electrode to the junction between the diodes and the resistoia Theemitter electrode of the transistor is connected togthe output terminalin the tens register 810 corresponding to th'e tens digit of thedirectory number of the subscriberline to which the crosspointcorresponds: Thus, as th'e crosspoiht referred to' andi illiistratediabove corresponds I to the subscriber: line' i 301 .1 for: which: thetens digit; of thefi directorynumberis: zero, the emitteri electrodeofthe transistor 403-1 is connected'to tliebutput conductor of th'el 0stage of the -'tens register, that. is, the conductor RT-tlvia= I the-resis tor 407. As illus'-: trated in Fig; 4, the' emitter electrodesof'the transistors T403-1' 'throu'gh T403-0; whichj'are respectivelyassociated-With F the 'c'rosspoints" corresponding: to thesubscriberlines 'for which the tens digit :of the directory number iszero; are all connectedi tol the' conductor RT-0 via a resistor 407;.Similarly; the output conductor RT-0 from the tens register- 81'0' isconnected via the resistor" 497 to the"' emitter[ electrodes"of the'transistor- T493-1. through T4 0 which are c'qnnec ted to thecrosspointscorre spending- "to the subscriber" lines for which the tensdigit is nine. From these examples it'may be seen thattheoutputiconduet'ors T-SdOWn thrOugh RT-I-are=respectively cQnncctedWOtlie emitter electrodes ofi'th c groups of 't'ransistors to whichthe-tens digit's of- =the relatedsubscribei lines correspondfi 1. Thebase electrodeoffthe: transistor T403-1 like the" base electrodes of theother transistors corresponding to theisiibs'criber lines for; whichthe" units digit of the' directory number is-orie, is connected-muteoutput con diic'tor' RU -1 of'the unit's register 830, which conductoris connected-to the-'"lw'stage thereof. -The'output con;

ductors RU-2" frQm the unitsre'gister830-is connected to thebaseelectrodes of --'the "transistors T413-2 throughT403-2-associatedfwith-1crosspoints for which the corre' spondingsubscriber lines have a directory "number for which) thefunits''digitis'two. Similarly; the conductors RU-3 through RU-l) areconne'cte'd to the baseelectrodes of the transistors correspondinglyassociated with-the units digits of the" directory number three throu'gh zero;

Responsive to the'application of the potentials on the eonductorqRT-ll:and; on. the; conductor RU-l, the tram sister. T403 1 is renderedconductive during the periods ottth'e simultaneously occu rring"negative and positive pulses thereby applying output: current to thecollector gl io u i it e' t r l d bf PH a Q -J 11 i arr exemplary,arrangement ,where the' pui s jsj v fi njd IS i are era livemicreseconaauraaen in"ea'ch'fifty n'lic ro'

